Nonwoven webs formed by nonwoven extrusion processes such as, for example, meltblowing processes and spunbonding processes may be manufactured into products and components of products so inexpensively that the products could be viewed as disposable after only one or a few uses. Representatives of such products include disposable absorbent articles, such as diapers, incontinence briefs, training pants, feminine hygiene garments, and the like.
Infants and other incontinent individuals wear disposable absorbent articles such as diapers to receive and contain urine and other body exudates. Absorbent articles function both to contain the discharged materials and to isolate these materials from the body of the wearer and from the wearer's garments and bed clothing. Disposable absorbent articles having many different basic designs are known to the art.
A typical absorbent article includes a liquid pervious topsheet, a liquid impervious backsheet joined to the topsheet, and an absorbent core positioned between the topsheet and the backsheet. Nonwoven webs are often used as the topsheet because they are liquid pervious and provide a skin friendly surface. However, in certain uses nonwoven webs do not function all that well as a topsheet as body exudates sometimes hang-up or get caught in the nonwoven web and thus become trapped against the wearer's skin. One solution to the aforementioned problem is to provide apertures in the nonwoven web so that body exudates may readily penetrate through the nonwoven web and into the underlying absorbent core. Unfortunately, certain techniques used to form apertured nonwoven webs are either costly, create an undesirable harsh feeling against the wearer's skin, or are subject to tearing, particularly when the apertured nonwoven web is to be used as a topsheet on a disposable absorbent article.
One economical method of forming apertures in a nonwoven to solve the above-mentioned problems taught in U.S. Pat. No. 5,628,097, entitled Method For Selectively Aperturing a Nonwoven Web, which issued May 13, 1997 to Curro et al.; and, U.S. Pat. No. 5,916,661, entitled Selectively Apertured Nonwoven Web, which issued Jun. 29, 1999 to Curro et al., both of which are hereby incorporated herein by reference. The nonwoven webs taught by both Curro et al. patents have proven to be effective as topsheets in disposable absorbent garments, including disposable diapers. The apertures formed by the processes described are effective for management of higher viscosity body wastes, for example.
Apertured nonwoven webs can be made by several other processes as well, for example by i) slitting and stretching as described in U.S. Pat. No. 5,714,107, entitled Perforated Nonwoven Fabrics; ii) perforating with patterned rolls as in European Patent No. EP-A-0 955 159, entitled Method for Forming Apertured Laminate Web; iii) hydroentangling or hydroaperturing as described in U.S. Pat. No. 5,414,914, entitled Process for Producing Apertured Nonwoven Fabric; and iv) hot needling as described in U.S. Pat. No. 4,469,734, entitled Microfibre Web Products.
The open area and hole size are two important properties of apertured webs for use as a topsheet in a disposable absorbent article. In order to effectively accept viscous body exudates, the open area of each aperture needs to be greater than 1 mm2, preferably greater than 2 mm2 and most preferably greater than 3 mm2. Also, the total open area of the entire topsheet is preferably at least about 15%. Ideally, the apertures, or holes should be circular, or almost circular. However, if the holes are oval shaped, the hole aspect ratio, which is defined as the ratio of the major axis to the minor axis of the oval, should be less than 8, preferably less than 6 and most preferably less than 4.
While producing high quality, economical apertured nonwoven webs, the webs taught by Curro et al., as well as webs made by the other methods listed above suffer from the drawback that with known technology, the webs exhibit a cross-machine direction extensibility that limits their use in certain high-extensible disposable garment products. For example, as disposable absorbent garments are improved, extensibility of the various components becomes more important. In disposable diapers, for example, it is desirable to have extensible chassis components such as the backsheet and the topsheet. Extensible components permit a wider range of unrestricted movement of the wearer, such as a baby. Higher extensibility results in easier application, less restriction of the skin, and higher comfort levels for the wearer.
Current apertured nonwovens typically have essentially the same extensibility of the base, i.e., non-apertured nonwoven. That is, the aperturing process does not improve the extensibility characteristics. Even apertured nonwovens designed specifically for disposable absorbent articles, such as those manufactured according to the teachings of Curro et al., typically have cross-machine direction extensibility of about 50% at a loading of 25 g/in. (25 g/2.54 cm, which is about 10 g/cm) tensile force. That is, an apertured nonwoven web, such as for a diaper topsheet, having a cross-machine direction dimension of 100 cm could elongate in that direction up to about 150 cm under a tensile loading of about 10 g/cm (10 grams per linear centimeter applied to each opposing edge being grasped to put the web in tensile loading) without significant degradation in performance or material integrity.
Certain apertured nonwoven webs may exhibit sufficient extensibility, but, nevertheless, fail to maintain adequate hole size and shape upon extension. For example, apertured nonwoven webs that are made by the slitting and stretching approach can potentially be made extensible by consolidating the slit web, i.e. stretching it in the machine direction to make it neck to a narrower width in cross machine direction. This approach, however, decreases the hole size substantially and will also increase the hole aspect ratio. Another potential approach is to consolidate the web and then slit and stretch it. However, when such a web is stretched in cross machine direction, the web will tend to return to its unnecked state prior to the holes opening up, thus losing the benefit of consolidation. Yet another potential approach may be to consolidate the web and punch holes in it via processes like hot needling. These webs are unsuitable for diaper application as they are not soft. This is because of the thick melt edges that are left behind where the apertures are formed.
Accordingly, it would be desirable to have an apertured nonwoven web that has hole size greater than 2 m2, total open area greater than 15% and hole aspect ratio less than 6 and that can, in addition, exhibit cross-direction extensibility greater than about 50% at about 10 g/cm tensile force.
Additionally, it would be desirable to have an apertured nonwoven web suitable for use as a topsheet in a disposable diaper, that can exhibit cross-direction extensibility greater than about 70% at 10 g/cm tensile force.
Further, it would be desirable to have an economical method for making an apertured nonwoven web that can exhibit cross-direction extensibility greater than about 70% at 10 g/cm tensile force.